Sulfite cooking method for the production of cellulose from materials containing lignocellulose with recovery of the cooking chemicals

Abstract

A sulphite cooking process is described for the production of pulp from materials containing lignocelluloses, with recovery of the cooking chemicals, in which the cooking, the blowing, the washing and the bleaching are performed sucessively. The waste liquor is subjected to several thermal treatments for the recovery of the cooking chemicals. For the cooking of the lignocellulosic materials, alkaline sulphite solutions are used, to which one or, in mixture, several low-boiling solvents are added, as well as at least one compound suitable as a redox catalyst.

We claim: 
     
       1. In a sulfite cooking process for the production of pulp from lignocellulose materials wherein said process includes sequential steps of cooking, blowing, washing, and bleaching, and wherein solutions used in the cooking process are recycled in the process, the improvement which comprises cooking of the lignocellulose materials with a cooking solution of a water-soluble alkaline sulfite compound, and alcohol, and a quinone redox catalyst wherein said alcohol comprises about 10 to 60% of said cooking solution; and wherein said water-soluble alkaline sulfite compound and said alcohol are recovered from one or more of said steps subsequent to said cooking step, and wherein the recovered sulfite compound and alcohol are recycled to said cooking solution for further cooking of the lignocellulose materials. 
     
     
       2. The process according to claim 1, characterized in that anthraquinone or anthrahydroquinone is added to the cooking solution as a redox catalyst. 
     
     
       3. A sulfite cooking process for the production of pulp from lignocellulosic materials including cooking, blowing, pulp washing, and bleaching steps comprising: (A) cooking said lignocellulosic materials with a cooking solution containing at least one water-soluble alkaline sulfite compound, an alcohol, and a quinone compound redox catalyst, to form a pulp cooking liquor wherein said alcohol comprises about 10 to 60% of said cooking solution;   (B) washing said cooking liquor and thereby separating said pulp cooking liquor into a pulp component and a black liquor component;   (C) evaporating said black liquor to form a concentrated black liquor, and an alcohol for recycling into said cooking solution of step A;   (D) thermally degrading said concentrated black liquor in a reducing atmosphere to form a solid residue;   (E) leaching said solid residue to form an alkali carbonate, and an alkali sulfite compound for recycling into said cooking solution of step A; and   (F) sulfiting said alkali carbonate with sulphur dioxide to form an alkali sulphite compound for recycling into said cooking solution of step A.   
     
     
       4. Process according to claim 3, characterized in that anthraquinone or anthrahydroquinone is added to the cooking solution as redox catalyst. 
     
     
       5. The process according to claim 3, characterized in that said quinone compound is added to the cooking solution in the amount of about 0.05 to 0.5% of the input dry plant raw material. 
     
     
       6. Process according to claim 3, characterized in that a pure monosulfite solution on a basis of sodium or ammonium is used for the pulping process. 
     
     
       7. Process accordance to claim 6, characterized in that corresponding carbonates with a predominant content of said monosulfite solution is added to the cooking liquor. 
     
     
       8. The process according to claim 6, characterized in that corresponding hydroxides with a predominant content of the monosulfite solution is added to said cooking liquor. 
     
     
       9. Process according to claim 3, characterized in that the ratio of said lignocellulosic material to the total cooking liquor is chosen between 1:2 and 1:8. 
     
     
       10. Process according to claim 9, characterized in that the maximum cooking temperature is set between 160° and 190° C. and the pressure in the range between 8 and 16 bar. 
     
     
       11. Process according to claim 9, characterized in that the cooking time is in the range between 30 and 240 minutes. 
     
     
       12. Process according to claim 10, characterized in that said alkali carbonates are dissolved out of said solid residue of the thermal degradation by means of water. 
     
     
       13. Process according claim 12, characterized in that the carbon content of said solid residue is separated by filtration and fed as fuel to the oxidation of the sulfur compounds in the exhaust gases of the thermal degradation. 
     
     
       14. The process of claim 3, further characterized in that said bleaching step is chlorine free, and effluents from said bleaching step are recycled into at least one of the following steps: said pulp cooking liquor of said step A, and the thermal degradation process of step D. 
     
     
       15. Process according to claim 13, characterized in that the thermal degradation of the cooking black liquor is performed in a plurality of stages in a reducing atmosphere, and the solid products formed in the first stage are continually removed from the heat-transfer surfaces of the reactor and comminuted in the following stages. 
     
     
       16. Process according to claim 15, characterized in that the thermal degradation of the cooking liquor is performed by indirect heating with a substantially horizontal stream of substance, and with a component at right angles thereto for a stirring of the solids. 
     
     
       17. Process according to claim 16, characterized in that the thermal degradation is performed in a reducing atmosphere at temperatures between 500° and 850° C. for a retention time between 30 and 120 minutes. 
     
     
       18. The process of claim 3, further characterized in that the carbon content of the leached solid residue is recycled and used as an activating adjuvant and absorber in the biological purification of bleaching effluents from the bleaching step. 
     
     
       19. A sulfite cooking process for the production of pulp from lignocellulosic materials including cooking, blowing, pulp washing, and bleaching steps comprising: (A) cooking said lignocellulosic materials with a cooking solution containing at least one water-soluble alkaline sulfite compound, an alcohol, and a quinone compound redox catalyst to form a pulp cooking liquor wherein said alcohol comprises about 10 to 60% of said cooking solution;   (B) washing said cooking liquor and thereby separating said pulp cooking liquor into a pulp component and a black liquor component;   (C) evaporating said black liquor to form a concentrated black liquor, and an alcohol for recycling into said cooking solution of step A;   (D) thermally degrading said concentrated black liquor in a reducing atmosphere to form a melt containing Na 2  S and Na 2  CO 3  ;   (E) converting said Na 2  S into Na 2  CO 3  and H 2  S and oxidizing said H 2  S into SO 2  ; and   (F) sulfiting said alkali carbonate with said sulphur dioxide to form a sulphite compound for recycling into said cooking solution of step A.